The present invention relates to a system for controlling the speed of an electric cooling fan, including an impeller driven by an electric DC motor and associated with one or more heat exchangers mounted in a motor vehicle, in such a way that the forward displacement of the motor vehicle is such as to cause a flow of air which impinges on the impeller of the electric fan, causing a rotation thereof in the same direction as the rotation caused by the associated electric motor.
More specifically, the invention relates to a control system of this kind, comprising: a driving circuit for the motor of the electric fan, coupled to the electrical system of the motor vehicle and comprising a plurality of controlled electronic switches, and an electronic control unit arranged to control the driving circuit so as to cause the flow in the motor of the electric fan of a variable average current capable of making the motor of the electric fan reach a required rotation speed in accordance with a predetermined relationship or function.
FIG. 1 of the attached drawings is a schematic representation of the architecture of a control system of this kind according to the prior art. Incidentally, a control system according to the present invention has essentially the same architecture.
In FIG. 1, EP indicates the whole of what is known as a heat exchanger “package”, mounted in the front compartment under the bonnet of a motor vehicle, and associated with an electric fan indicated as a whole by EF. This electric fan comprises a bladed impeller BI, of a known type, rotated by an electric DC motor EM. This motor is, for example, a brushless motor, or a motor with brushes, and is driven by a circuit (or “driver”) MDC which is connected to the electrical system of the motor vehicle which includes a battery B.
The driving circuit MDC is controlled by an electronic control unit ECU which can be, for example, the electronic control unit associated with the internal combustion engine of the motor vehicle. This unit receives numerous pieces of information from various sensor devices, indicated as a whole by S in FIG. 1.
The control unit ECU is designed to control the driving circuit MDC, according to a predetermined relationship or function, such as that illustrated in a qualitative manner in FIG. 2 by way of example, thus causing a variable average current to flow in the motor EM in such a way that the motor is made to reach the rotation speed n (the required speed).
In FIG. 2, the values of a control magnitude are shown on the horizontal axis, and the corresponding values of the required speed n of the motor EM are shown on the vertical axis. For example, the control magnitude or parameter may be the duty cycle of a fixed frequency square wave control signal.
As mentioned above, when the motor vehicle is displaced in a forward direction, a flow of air is naturally created, and passes through the exchanger package EP until it impinges on the impeller BI of the electric fan EF, causing it to rotate in the direction of the rotation imparted to the impeller by the associated electric motor EM. The action of this air current on the impeller BI is known as “wind-milling”.
When the motor vehicle is moving forwards at a low speed, the action of the aforesaid air current causes a reduction of the torque that has to be developed by the motor EM in order to keep the impeller BI rotating at the desired speed. This results in a reduction of the average current and of the consumption of power from the battery B.
When the vehicle is moving forwards at higher speeds, the driving torque acting on the impeller BI of the electric fan as a result of wind-milling can increase to a point where the impeller BI starts to rotate at a higher speed than the requested speed n.
In the existing systems for controlling the rotation speed of an electric fan in such a condition, the impeller BI is allowed to rotate freely. Although this approach is simple, it has a number of drawbacks, including the acoustic noise and vibrations that are generated, and the fact that the heat exchanger package EP can be cooled more than necessary which may result in greater air pollution.